Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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sys/kern/kern_mutex.c
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1 /*- 2 * Copyright (c) 1998 Berkeley Software Design, Inc. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 1. Redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer. 9 * 2. Redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution. 12 * 3. Berkeley Software Design Inc's name may not be used to endorse or 13 * promote products derived from this software without specific prior 14 * written permission. 15 * 16 * THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``AS IS'' AND 17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19 * ARE DISCLAIMED. IN NO EVENT SHALL BERKELEY SOFTWARE DESIGN INC BE LIABLE 20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 * 28 * from BSDI $Id: mutex_witness.c,v 1.1.2.20 2000/04/27 03:10:27 cp Exp $ 29 * and BSDI $Id: synch_machdep.c,v 2.3.2.39 2000/04/27 03:10:25 cp Exp $ 30 */ 31 32 /* 33 * Machine independent bits of mutex implementation. 34 */ 35 36 #include <sys/cdefs.h> 37 __FBSDID("$FreeBSD: releng/6.4/sys/kern/kern_mutex.c 172355 2007-09-27 20:24:56Z jhb $"); 38 39 #include "opt_adaptive_mutexes.h" 40 #include "opt_ddb.h" 41 #include "opt_mprof.h" 42 #include "opt_mutex_wake_all.h" 43 #include "opt_sched.h" 44 45 #include <sys/param.h> 46 #include <sys/systm.h> 47 #include <sys/bus.h> 48 #include <sys/conf.h> 49 #include <sys/kdb.h> 50 #include <sys/kernel.h> 51 #include <sys/ktr.h> 52 #include <sys/lock.h> 53 #include <sys/malloc.h> 54 #include <sys/mutex.h> 55 #include <sys/proc.h> 56 #include <sys/resourcevar.h> 57 #include <sys/sched.h> 58 #include <sys/sbuf.h> 59 #include <sys/sysctl.h> 60 #include <sys/turnstile.h> 61 #include <sys/vmmeter.h> 62 63 #include <machine/atomic.h> 64 #include <machine/bus.h> 65 #include <machine/clock.h> 66 #include <machine/cpu.h> 67 68 #include <ddb/ddb.h> 69 70 #include <fs/devfs/devfs_int.h> 71 72 #include <vm/vm.h> 73 #include <vm/vm_extern.h> 74 75 /* 76 * Force MUTEX_WAKE_ALL for now. 77 * single thread wakeup needs fixes to avoid race conditions with 78 * priority inheritance. 79 */ 80 #ifndef MUTEX_WAKE_ALL 81 #define MUTEX_WAKE_ALL 82 #endif 83 84 /* 85 * Internal utility macros. 86 */ 87 #define mtx_unowned(m) ((m)->mtx_lock == MTX_UNOWNED) 88 89 #define mtx_owner(m) (mtx_unowned((m)) ? NULL \ 90 : (struct thread *)((m)->mtx_lock & MTX_FLAGMASK)) 91 92 #ifdef DDB 93 static void db_show_mtx(struct lock_object *lock); 94 #endif 95 96 /* 97 * Lock classes for sleep and spin mutexes. 98 */ 99 struct lock_class lock_class_mtx_sleep = { 100 "sleep mutex", 101 LC_SLEEPLOCK | LC_RECURSABLE, 102 #ifdef DDB 103 db_show_mtx 104 #endif 105 }; 106 struct lock_class lock_class_mtx_spin = { 107 "spin mutex", 108 LC_SPINLOCK | LC_RECURSABLE, 109 #ifdef DDB 110 db_show_mtx 111 #endif 112 }; 113 114 /* 115 * System-wide mutexes 116 */ 117 struct mtx sched_lock; 118 struct mtx Giant; 119 120 #ifdef MUTEX_PROFILING 121 SYSCTL_NODE(_debug, OID_AUTO, mutex, CTLFLAG_RD, NULL, "mutex debugging"); 122 SYSCTL_NODE(_debug_mutex, OID_AUTO, prof, CTLFLAG_RD, NULL, "mutex profiling"); 123 static int mutex_prof_enable = 0; 124 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, enable, CTLFLAG_RW, 125 &mutex_prof_enable, 0, "Enable tracing of mutex holdtime"); 126 127 struct mutex_prof { 128 const char *name; 129 const char *file; 130 int line; 131 uintmax_t cnt_max; 132 uintmax_t cnt_tot; 133 uintmax_t cnt_cur; 134 uintmax_t cnt_contest_holding; 135 uintmax_t cnt_contest_locking; 136 struct mutex_prof *next; 137 }; 138 139 /* 140 * mprof_buf is a static pool of profiling records to avoid possible 141 * reentrance of the memory allocation functions. 142 * 143 * Note: NUM_MPROF_BUFFERS must be smaller than MPROF_HASH_SIZE. 144 */ 145 #ifdef MPROF_BUFFERS 146 #define NUM_MPROF_BUFFERS MPROF_BUFFERS 147 #else 148 #define NUM_MPROF_BUFFERS 1000 149 #endif 150 static struct mutex_prof mprof_buf[NUM_MPROF_BUFFERS]; 151 static int first_free_mprof_buf; 152 #ifndef MPROF_HASH_SIZE 153 #define MPROF_HASH_SIZE 1009 154 #endif 155 #if NUM_MPROF_BUFFERS >= MPROF_HASH_SIZE 156 #error MPROF_BUFFERS must be larger than MPROF_HASH_SIZE 157 #endif 158 static struct mutex_prof *mprof_hash[MPROF_HASH_SIZE]; 159 /* SWAG: sbuf size = avg stat. line size * number of locks */ 160 #define MPROF_SBUF_SIZE 256 * 400 161 162 static int mutex_prof_acquisitions; 163 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, acquisitions, CTLFLAG_RD, 164 &mutex_prof_acquisitions, 0, "Number of mutex acquistions recorded"); 165 static int mutex_prof_records; 166 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, records, CTLFLAG_RD, 167 &mutex_prof_records, 0, "Number of profiling records"); 168 static int mutex_prof_maxrecords = NUM_MPROF_BUFFERS; 169 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, maxrecords, CTLFLAG_RD, 170 &mutex_prof_maxrecords, 0, "Maximum number of profiling records"); 171 static int mutex_prof_rejected; 172 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, rejected, CTLFLAG_RD, 173 &mutex_prof_rejected, 0, "Number of rejected profiling records"); 174 static int mutex_prof_hashsize = MPROF_HASH_SIZE; 175 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, hashsize, CTLFLAG_RD, 176 &mutex_prof_hashsize, 0, "Hash size"); 177 static int mutex_prof_collisions = 0; 178 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, collisions, CTLFLAG_RD, 179 &mutex_prof_collisions, 0, "Number of hash collisions"); 180 181 /* 182 * mprof_mtx protects the profiling buffers and the hash. 183 */ 184 static struct mtx mprof_mtx; 185 MTX_SYSINIT(mprof, &mprof_mtx, "mutex profiling lock", MTX_SPIN | MTX_QUIET); 186 187 static u_int64_t 188 nanoseconds(void) 189 { 190 struct timespec tv; 191 192 nanotime(&tv); 193 return (tv.tv_sec * (u_int64_t)1000000000 + tv.tv_nsec); 194 } 195 196 static int 197 dump_mutex_prof_stats(SYSCTL_HANDLER_ARGS) 198 { 199 struct sbuf *sb; 200 int error, i; 201 static int multiplier = 1; 202 203 if (first_free_mprof_buf == 0) 204 return (SYSCTL_OUT(req, "No locking recorded", 205 sizeof("No locking recorded"))); 206 207 retry_sbufops: 208 sb = sbuf_new(NULL, NULL, MPROF_SBUF_SIZE * multiplier, SBUF_FIXEDLEN); 209 sbuf_printf(sb, "\n%6s %12s %11s %5s %12s %12s %s\n", 210 "max", "total", "count", "avg", "cnt_hold", "cnt_lock", "name"); 211 /* 212 * XXX this spinlock seems to be by far the largest perpetrator 213 * of spinlock latency (1.6 msec on an Athlon1600 was recorded 214 * even before I pessimized it further by moving the average 215 * computation here). 216 */ 217 mtx_lock_spin(&mprof_mtx); 218 for (i = 0; i < first_free_mprof_buf; ++i) { 219 sbuf_printf(sb, "%6ju %12ju %11ju %5ju %12ju %12ju %s:%d (%s)\n", 220 mprof_buf[i].cnt_max / 1000, 221 mprof_buf[i].cnt_tot / 1000, 222 mprof_buf[i].cnt_cur, 223 mprof_buf[i].cnt_cur == 0 ? (uintmax_t)0 : 224 mprof_buf[i].cnt_tot / (mprof_buf[i].cnt_cur * 1000), 225 mprof_buf[i].cnt_contest_holding, 226 mprof_buf[i].cnt_contest_locking, 227 mprof_buf[i].file, mprof_buf[i].line, mprof_buf[i].name); 228 if (sbuf_overflowed(sb)) { 229 mtx_unlock_spin(&mprof_mtx); 230 sbuf_delete(sb); 231 multiplier++; 232 goto retry_sbufops; 233 } 234 } 235 mtx_unlock_spin(&mprof_mtx); 236 sbuf_finish(sb); 237 error = SYSCTL_OUT(req, sbuf_data(sb), sbuf_len(sb) + 1); 238 sbuf_delete(sb); 239 return (error); 240 } 241 SYSCTL_PROC(_debug_mutex_prof, OID_AUTO, stats, CTLTYPE_STRING | CTLFLAG_RD, 242 NULL, 0, dump_mutex_prof_stats, "A", "Mutex profiling statistics"); 243 244 static int 245 reset_mutex_prof_stats(SYSCTL_HANDLER_ARGS) 246 { 247 int error, v; 248 249 if (first_free_mprof_buf == 0) 250 return (0); 251 252 v = 0; 253 error = sysctl_handle_int(oidp, &v, 0, req); 254 if (error) 255 return (error); 256 if (req->newptr == NULL) 257 return (error); 258 if (v == 0) 259 return (0); 260 261 mtx_lock_spin(&mprof_mtx); 262 bzero(mprof_buf, sizeof(*mprof_buf) * first_free_mprof_buf); 263 bzero(mprof_hash, sizeof(struct mtx *) * MPROF_HASH_SIZE); 264 first_free_mprof_buf = 0; 265 mtx_unlock_spin(&mprof_mtx); 266 return (0); 267 } 268 SYSCTL_PROC(_debug_mutex_prof, OID_AUTO, reset, CTLTYPE_INT | CTLFLAG_RW, 269 NULL, 0, reset_mutex_prof_stats, "I", "Reset mutex profiling statistics"); 270 #endif 271 272 /* 273 * Function versions of the inlined __mtx_* macros. These are used by 274 * modules and can also be called from assembly language if needed. 275 */ 276 void 277 _mtx_lock_flags(struct mtx *m, int opts, const char *file, int line) 278 { 279 280 MPASS(curthread != NULL); 281 KASSERT(m->mtx_lock != MTX_DESTROYED, 282 ("mtx_lock() of destroyed mutex @ %s:%d", file, line)); 283 KASSERT(LOCK_CLASS(&m->mtx_object) == &lock_class_mtx_sleep, 284 ("mtx_lock() of spin mutex %s @ %s:%d", m->mtx_object.lo_name, 285 file, line)); 286 WITNESS_CHECKORDER(&m->mtx_object, opts | LOP_NEWORDER | LOP_EXCLUSIVE, 287 file, line); 288 _get_sleep_lock(m, curthread, opts, file, line); 289 LOCK_LOG_LOCK("LOCK", &m->mtx_object, opts, m->mtx_recurse, file, 290 line); 291 WITNESS_LOCK(&m->mtx_object, opts | LOP_EXCLUSIVE, file, line); 292 curthread->td_locks++; 293 #ifdef MUTEX_PROFILING 294 /* don't reset the timer when/if recursing */ 295 if (m->mtx_acqtime == 0) { 296 m->mtx_filename = file; 297 m->mtx_lineno = line; 298 m->mtx_acqtime = mutex_prof_enable ? nanoseconds() : 0; 299 ++mutex_prof_acquisitions; 300 } 301 #endif 302 } 303 304 void 305 _mtx_unlock_flags(struct mtx *m, int opts, const char *file, int line) 306 { 307 308 MPASS(curthread != NULL); 309 KASSERT(m->mtx_lock != MTX_DESTROYED, 310 ("mtx_unlock() of destroyed mutex @ %s:%d", file, line)); 311 KASSERT(LOCK_CLASS(&m->mtx_object) == &lock_class_mtx_sleep, 312 ("mtx_unlock() of spin mutex %s @ %s:%d", m->mtx_object.lo_name, 313 file, line)); 314 curthread->td_locks--; 315 WITNESS_UNLOCK(&m->mtx_object, opts | LOP_EXCLUSIVE, file, line); 316 LOCK_LOG_LOCK("UNLOCK", &m->mtx_object, opts, m->mtx_recurse, file, 317 line); 318 mtx_assert(m, MA_OWNED); 319 #ifdef MUTEX_PROFILING 320 if (m->mtx_acqtime != 0) { 321 static const char *unknown = "(unknown)"; 322 struct mutex_prof *mpp; 323 u_int64_t acqtime, now; 324 const char *p, *q; 325 volatile u_int hash; 326 327 now = nanoseconds(); 328 acqtime = m->mtx_acqtime; 329 m->mtx_acqtime = 0; 330 if (now <= acqtime) 331 goto out; 332 for (p = m->mtx_filename; 333 p != NULL && strncmp(p, "../", 3) == 0; p += 3) 334 /* nothing */ ; 335 if (p == NULL || *p == '\0') 336 p = unknown; 337 for (hash = m->mtx_lineno, q = p; *q != '\0'; ++q) 338 hash = (hash * 2 + *q) % MPROF_HASH_SIZE; 339 mtx_lock_spin(&mprof_mtx); 340 for (mpp = mprof_hash[hash]; mpp != NULL; mpp = mpp->next) 341 if (mpp->line == m->mtx_lineno && 342 strcmp(mpp->file, p) == 0) 343 break; 344 if (mpp == NULL) { 345 /* Just exit if we cannot get a trace buffer */ 346 if (first_free_mprof_buf >= NUM_MPROF_BUFFERS) { 347 ++mutex_prof_rejected; 348 goto unlock; 349 } 350 mpp = &mprof_buf[first_free_mprof_buf++]; 351 mpp->name = mtx_name(m); 352 mpp->file = p; 353 mpp->line = m->mtx_lineno; 354 mpp->next = mprof_hash[hash]; 355 if (mprof_hash[hash] != NULL) 356 ++mutex_prof_collisions; 357 mprof_hash[hash] = mpp; 358 ++mutex_prof_records; 359 } 360 /* 361 * Record if the mutex has been held longer now than ever 362 * before. 363 */ 364 if (now - acqtime > mpp->cnt_max) 365 mpp->cnt_max = now - acqtime; 366 mpp->cnt_tot += now - acqtime; 367 mpp->cnt_cur++; 368 /* 369 * There's a small race, really we should cmpxchg 370 * 0 with the current value, but that would bill 371 * the contention to the wrong lock instance if 372 * it followed this also. 373 */ 374 mpp->cnt_contest_holding += m->mtx_contest_holding; 375 m->mtx_contest_holding = 0; 376 mpp->cnt_contest_locking += m->mtx_contest_locking; 377 m->mtx_contest_locking = 0; 378 unlock: 379 mtx_unlock_spin(&mprof_mtx); 380 } 381 out: 382 #endif 383 _rel_sleep_lock(m, curthread, opts, file, line); 384 } 385 386 void 387 _mtx_lock_spin_flags(struct mtx *m, int opts, const char *file, int line) 388 { 389 390 MPASS(curthread != NULL); 391 KASSERT(m->mtx_lock != MTX_DESTROYED, 392 ("mtx_lock_spin() of destroyed mutex @ %s:%d", file, line)); 393 KASSERT(LOCK_CLASS(&m->mtx_object) == &lock_class_mtx_spin, 394 ("mtx_lock_spin() of sleep mutex %s @ %s:%d", 395 m->mtx_object.lo_name, file, line)); 396 WITNESS_CHECKORDER(&m->mtx_object, opts | LOP_NEWORDER | LOP_EXCLUSIVE, 397 file, line); 398 _get_spin_lock(m, curthread, opts, file, line); 399 LOCK_LOG_LOCK("LOCK", &m->mtx_object, opts, m->mtx_recurse, file, 400 line); 401 WITNESS_LOCK(&m->mtx_object, opts | LOP_EXCLUSIVE, file, line); 402 } 403 404 void 405 _mtx_unlock_spin_flags(struct mtx *m, int opts, const char *file, int line) 406 { 407 408 MPASS(curthread != NULL); 409 KASSERT(m->mtx_lock != MTX_DESTROYED, 410 ("mtx_unlock_spin() of destroyed mutex @ %s:%d", file, line)); 411 KASSERT(LOCK_CLASS(&m->mtx_object) == &lock_class_mtx_spin, 412 ("mtx_unlock_spin() of sleep mutex %s @ %s:%d", 413 m->mtx_object.lo_name, file, line)); 414 WITNESS_UNLOCK(&m->mtx_object, opts | LOP_EXCLUSIVE, file, line); 415 LOCK_LOG_LOCK("UNLOCK", &m->mtx_object, opts, m->mtx_recurse, file, 416 line); 417 mtx_assert(m, MA_OWNED); 418 _rel_spin_lock(m); 419 } 420 421 /* 422 * The important part of mtx_trylock{,_flags}() 423 * Tries to acquire lock `m.' If this function is called on a mutex that 424 * is already owned, it will recursively acquire the lock. 425 */ 426 int 427 _mtx_trylock(struct mtx *m, int opts, const char *file, int line) 428 { 429 int rval; 430 431 MPASS(curthread != NULL); 432 KASSERT(m->mtx_lock != MTX_DESTROYED, 433 ("mtx_trylock() of destroyed mutex @ %s:%d", file, line)); 434 KASSERT(LOCK_CLASS(&m->mtx_object) == &lock_class_mtx_sleep, 435 ("mtx_trylock() of spin mutex %s @ %s:%d", m->mtx_object.lo_name, 436 file, line)); 437 438 if (mtx_owned(m) && (m->mtx_object.lo_flags & LO_RECURSABLE) != 0) { 439 m->mtx_recurse++; 440 atomic_set_ptr(&m->mtx_lock, MTX_RECURSED); 441 rval = 1; 442 } else 443 rval = _obtain_lock(m, (uintptr_t)curthread); 444 445 LOCK_LOG_TRY("LOCK", &m->mtx_object, opts, rval, file, line); 446 if (rval) { 447 WITNESS_LOCK(&m->mtx_object, opts | LOP_EXCLUSIVE | LOP_TRYLOCK, 448 file, line); 449 curthread->td_locks++; 450 } 451 452 return (rval); 453 } 454 455 /* 456 * _mtx_lock_sleep: the tougher part of acquiring an MTX_DEF lock. 457 * 458 * We call this if the lock is either contested (i.e. we need to go to 459 * sleep waiting for it), or if we need to recurse on it. 460 */ 461 void 462 _mtx_lock_sleep(struct mtx *m, uintptr_t tid, int opts, const char *file, 463 int line) 464 { 465 #if defined(SMP) && !defined(NO_ADAPTIVE_MUTEXES) 466 volatile struct thread *owner; 467 #endif 468 uintptr_t v; 469 #ifdef KTR 470 int cont_logged = 0; 471 #endif 472 #ifdef MUTEX_PROFILING 473 int contested; 474 #endif 475 476 if (mtx_owned(m)) { 477 KASSERT((m->mtx_object.lo_flags & LO_RECURSABLE) != 0, 478 ("_mtx_lock_sleep: recursed on non-recursive mutex %s @ %s:%d\n", 479 m->mtx_object.lo_name, file, line)); 480 m->mtx_recurse++; 481 atomic_set_ptr(&m->mtx_lock, MTX_RECURSED); 482 if (LOCK_LOG_TEST(&m->mtx_object, opts)) 483 CTR1(KTR_LOCK, "_mtx_lock_sleep: %p recursing", m); 484 return; 485 } 486 487 if (LOCK_LOG_TEST(&m->mtx_object, opts)) 488 CTR4(KTR_LOCK, 489 "_mtx_lock_sleep: %s contested (lock=%p) at %s:%d", 490 m->mtx_object.lo_name, (void *)m->mtx_lock, file, line); 491 492 #ifdef MUTEX_PROFILING 493 contested = 0; 494 #endif 495 while (!_obtain_lock(m, tid)) { 496 #ifdef MUTEX_PROFILING 497 contested = 1; 498 atomic_add_int(&m->mtx_contest_holding, 1); 499 #endif 500 turnstile_lock(&m->mtx_object); 501 v = m->mtx_lock; 502 503 /* 504 * Check if the lock has been released while spinning for 505 * the turnstile chain lock. 506 */ 507 if (v == MTX_UNOWNED) { 508 turnstile_release(&m->mtx_object); 509 cpu_spinwait(); 510 continue; 511 } 512 513 #ifdef MUTEX_WAKE_ALL 514 MPASS(v != MTX_CONTESTED); 515 #else 516 /* 517 * The mutex was marked contested on release. This means that 518 * there are other threads blocked on it. Grab ownership of 519 * it and propagate its priority to the current thread if 520 * necessary. 521 */ 522 if (v == MTX_CONTESTED) { 523 m->mtx_lock = tid | MTX_CONTESTED; 524 turnstile_claim(&m->mtx_object); 525 break; 526 } 527 #endif 528 529 /* 530 * If the mutex isn't already contested and a failure occurs 531 * setting the contested bit, the mutex was either released 532 * or the state of the MTX_RECURSED bit changed. 533 */ 534 if ((v & MTX_CONTESTED) == 0 && 535 !atomic_cmpset_ptr(&m->mtx_lock, v, v | MTX_CONTESTED)) { 536 turnstile_release(&m->mtx_object); 537 cpu_spinwait(); 538 continue; 539 } 540 541 #if defined(SMP) && !defined(NO_ADAPTIVE_MUTEXES) 542 /* 543 * If the current owner of the lock is executing on another 544 * CPU, spin instead of blocking. 545 */ 546 owner = (struct thread *)(v & MTX_FLAGMASK); 547 #ifdef ADAPTIVE_GIANT 548 if (TD_IS_RUNNING(owner)) { 549 #else 550 if (m != &Giant && TD_IS_RUNNING(owner)) { 551 #endif 552 turnstile_release(&m->mtx_object); 553 while (mtx_owner(m) == owner && TD_IS_RUNNING(owner)) { 554 cpu_spinwait(); 555 } 556 continue; 557 } 558 #endif /* SMP && !NO_ADAPTIVE_MUTEXES */ 559 560 /* 561 * We definitely must sleep for this lock. 562 */ 563 mtx_assert(m, MA_NOTOWNED); 564 565 #ifdef KTR 566 if (!cont_logged) { 567 CTR6(KTR_CONTENTION, 568 "contention: %p at %s:%d wants %s, taken by %s:%d", 569 (void *)tid, file, line, m->mtx_object.lo_name, 570 WITNESS_FILE(&m->mtx_object), 571 WITNESS_LINE(&m->mtx_object)); 572 cont_logged = 1; 573 } 574 #endif 575 576 /* 577 * Block on the turnstile. 578 */ 579 turnstile_wait(&m->mtx_object, mtx_owner(m), 580 TS_EXCLUSIVE_QUEUE); 581 } 582 583 #ifdef KTR 584 if (cont_logged) { 585 CTR4(KTR_CONTENTION, 586 "contention end: %s acquired by %p at %s:%d", 587 m->mtx_object.lo_name, (void *)tid, file, line); 588 } 589 #endif 590 #ifdef MUTEX_PROFILING 591 if (contested) 592 m->mtx_contest_locking++; 593 m->mtx_contest_holding = 0; 594 #endif 595 return; 596 } 597 598 #ifdef SMP 599 /* 600 * _mtx_lock_spin: the tougher part of acquiring an MTX_SPIN lock. 601 * 602 * This is only called if we need to actually spin for the lock. Recursion 603 * is handled inline. 604 */ 605 void 606 _mtx_lock_spin(struct mtx *m, uintptr_t tid, int opts, const char *file, 607 int line) 608 { 609 int i = 0; 610 611 if (LOCK_LOG_TEST(&m->mtx_object, opts)) 612 CTR1(KTR_LOCK, "_mtx_lock_spin: %p spinning", m); 613 614 for (;;) { 615 if (_obtain_lock(m, tid)) 616 break; 617 618 /* Give interrupts a chance while we spin. */ 619 spinlock_exit(); 620 while (m->mtx_lock != MTX_UNOWNED) { 621 if (i++ < 10000000) { 622 cpu_spinwait(); 623 continue; 624 } 625 if (i < 60000000) 626 DELAY(1); 627 else if (!kdb_active && !panicstr) { 628 printf("spin lock %s held by %p for > 5 seconds\n", 629 m->mtx_object.lo_name, (void *)m->mtx_lock); 630 #ifdef WITNESS 631 witness_display_spinlock(&m->mtx_object, 632 mtx_owner(m)); 633 #endif 634 panic("spin lock held too long"); 635 } 636 cpu_spinwait(); 637 } 638 spinlock_enter(); 639 } 640 641 if (LOCK_LOG_TEST(&m->mtx_object, opts)) 642 CTR1(KTR_LOCK, "_mtx_lock_spin: %p spin done", m); 643 644 return; 645 } 646 #endif /* SMP */ 647 648 /* 649 * _mtx_unlock_sleep: the tougher part of releasing an MTX_DEF lock. 650 * 651 * We are only called here if the lock is recursed or contested (i.e. we 652 * need to wake up a blocked thread). 653 */ 654 void 655 _mtx_unlock_sleep(struct mtx *m, int opts, const char *file, int line) 656 { 657 struct turnstile *ts; 658 #ifndef PREEMPTION 659 struct thread *td, *td1; 660 #endif 661 662 if (mtx_recursed(m)) { 663 if (--(m->mtx_recurse) == 0) 664 atomic_clear_ptr(&m->mtx_lock, MTX_RECURSED); 665 if (LOCK_LOG_TEST(&m->mtx_object, opts)) 666 CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p unrecurse", m); 667 return; 668 } 669 670 turnstile_lock(&m->mtx_object); 671 ts = turnstile_lookup(&m->mtx_object); 672 if (LOCK_LOG_TEST(&m->mtx_object, opts)) 673 CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p contested", m); 674 675 #if defined(SMP) && !defined(NO_ADAPTIVE_MUTEXES) 676 if (ts == NULL) { 677 _release_lock_quick(m); 678 if (LOCK_LOG_TEST(&m->mtx_object, opts)) 679 CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p no sleepers", m); 680 turnstile_release(&m->mtx_object); 681 return; 682 } 683 #else 684 MPASS(ts != NULL); 685 #endif 686 #ifndef PREEMPTION 687 /* XXX */ 688 td1 = turnstile_head(ts, TS_EXCLUSIVE_QUEUE); 689 #endif 690 #ifdef MUTEX_WAKE_ALL 691 turnstile_broadcast(ts, TS_EXCLUSIVE_QUEUE); 692 _release_lock_quick(m); 693 #else 694 if (turnstile_signal(ts, TS_EXCLUSIVE_QUEUE)) { 695 _release_lock_quick(m); 696 if (LOCK_LOG_TEST(&m->mtx_object, opts)) 697 CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p not held", m); 698 } else { 699 m->mtx_lock = MTX_CONTESTED; 700 if (LOCK_LOG_TEST(&m->mtx_object, opts)) 701 CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p still contested", 702 m); 703 } 704 #endif 705 turnstile_unpend(ts, TS_EXCLUSIVE_LOCK); 706 707 #ifndef PREEMPTION 708 /* 709 * XXX: This is just a hack until preemption is done. However, 710 * once preemption is done we need to either wrap the 711 * turnstile_signal() and release of the actual lock in an 712 * extra critical section or change the preemption code to 713 * always just set a flag and never do instant-preempts. 714 */ 715 td = curthread; 716 if (td->td_critnest > 0 || td1->td_priority >= td->td_priority) 717 return; 718 mtx_lock_spin(&sched_lock); 719 if (!TD_IS_RUNNING(td1)) { 720 #ifdef notyet 721 if (td->td_ithd != NULL) { 722 struct ithd *it = td->td_ithd; 723 724 if (it->it_interrupted) { 725 if (LOCK_LOG_TEST(&m->mtx_object, opts)) 726 CTR2(KTR_LOCK, 727 "_mtx_unlock_sleep: %p interrupted %p", 728 it, it->it_interrupted); 729 intr_thd_fixup(it); 730 } 731 } 732 #endif 733 if (LOCK_LOG_TEST(&m->mtx_object, opts)) 734 CTR2(KTR_LOCK, 735 "_mtx_unlock_sleep: %p switching out lock=%p", m, 736 (void *)m->mtx_lock); 737 738 mi_switch(SW_INVOL, NULL); 739 if (LOCK_LOG_TEST(&m->mtx_object, opts)) 740 CTR2(KTR_LOCK, "_mtx_unlock_sleep: %p resuming lock=%p", 741 m, (void *)m->mtx_lock); 742 } 743 mtx_unlock_spin(&sched_lock); 744 #endif 745 746 return; 747 } 748 749 /* 750 * All the unlocking of MTX_SPIN locks is done inline. 751 * See the _rel_spin_lock() macro for the details. 752 */ 753 754 /* 755 * The backing function for the INVARIANTS-enabled mtx_assert() 756 */ 757 #ifdef INVARIANT_SUPPORT 758 void 759 _mtx_assert(struct mtx *m, int what, const char *file, int line) 760 { 761 762 if (panicstr != NULL || dumping) 763 return; 764 switch (what) { 765 case MA_OWNED: 766 case MA_OWNED | MA_RECURSED: 767 case MA_OWNED | MA_NOTRECURSED: 768 if (!mtx_owned(m)) 769 panic("mutex %s not owned at %s:%d", 770 m->mtx_object.lo_name, file, line); 771 if (mtx_recursed(m)) { 772 if ((what & MA_NOTRECURSED) != 0) 773 panic("mutex %s recursed at %s:%d", 774 m->mtx_object.lo_name, file, line); 775 } else if ((what & MA_RECURSED) != 0) { 776 panic("mutex %s unrecursed at %s:%d", 777 m->mtx_object.lo_name, file, line); 778 } 779 break; 780 case MA_NOTOWNED: 781 if (mtx_owned(m)) 782 panic("mutex %s owned at %s:%d", 783 m->mtx_object.lo_name, file, line); 784 break; 785 default: 786 panic("unknown mtx_assert at %s:%d", file, line); 787 } 788 } 789 #endif 790 791 /* 792 * The MUTEX_DEBUG-enabled mtx_validate() 793 * 794 * Most of these checks have been moved off into the LO_INITIALIZED flag 795 * maintained by the witness code. 796 */ 797 #ifdef MUTEX_DEBUG 798 799 void mtx_validate(struct mtx *); 800 801 void 802 mtx_validate(struct mtx *m) 803 { 804 805 /* 806 * XXX: When kernacc() does not require Giant we can reenable this check 807 */ 808 #ifdef notyet 809 /* 810 * XXX - When kernacc() is fixed on the alpha to handle K0_SEG memory properly 811 * we can re-enable the kernacc() checks. 812 */ 813 #ifndef __alpha__ 814 /* 815 * Can't call kernacc() from early init386(), especially when 816 * initializing Giant mutex, because some stuff in kernacc() 817 * requires Giant itself. 818 */ 819 if (!cold) 820 if (!kernacc((caddr_t)m, sizeof(m), 821 VM_PROT_READ | VM_PROT_WRITE)) 822 panic("Can't read and write to mutex %p", m); 823 #endif 824 #endif 825 } 826 #endif 827 828 /* 829 * General init routine used by the MTX_SYSINIT() macro. 830 */ 831 void 832 mtx_sysinit(void *arg) 833 { 834 struct mtx_args *margs = arg; 835 836 mtx_init(margs->ma_mtx, margs->ma_desc, NULL, margs->ma_opts); 837 } 838 839 /* 840 * Mutex initialization routine; initialize lock `m' of type contained in 841 * `opts' with options contained in `opts' and name `name.' The optional 842 * lock type `type' is used as a general lock category name for use with 843 * witness. 844 */ 845 void 846 mtx_init(struct mtx *m, const char *name, const char *type, int opts) 847 { 848 struct lock_class *class; 849 int flags; 850 851 MPASS((opts & ~(MTX_SPIN | MTX_QUIET | MTX_RECURSE | 852 MTX_NOWITNESS | MTX_DUPOK)) == 0); 853 854 #ifdef MUTEX_DEBUG 855 /* Diagnostic and error correction */ 856 mtx_validate(m); 857 #endif 858 859 /* Determine lock class and lock flags. */ 860 if (opts & MTX_SPIN) 861 class = &lock_class_mtx_spin; 862 else 863 class = &lock_class_mtx_sleep; 864 flags = 0; 865 if (opts & MTX_QUIET) 866 flags |= LO_QUIET; 867 if (opts & MTX_RECURSE) 868 flags |= LO_RECURSABLE; 869 if ((opts & MTX_NOWITNESS) == 0) 870 flags |= LO_WITNESS; 871 if (opts & MTX_DUPOK) 872 flags |= LO_DUPOK; 873 874 /* Initialize mutex. */ 875 m->mtx_lock = MTX_UNOWNED; 876 m->mtx_recurse = 0; 877 #ifdef MUTEX_PROFILING 878 m->mtx_acqtime = 0; 879 m->mtx_filename = NULL; 880 m->mtx_lineno = 0; 881 m->mtx_contest_holding = 0; 882 m->mtx_contest_locking = 0; 883 #endif 884 885 lock_init(&m->mtx_object, class, name, type, flags); 886 } 887 888 /* 889 * Remove lock `m' from all_mtx queue. We don't allow MTX_QUIET to be 890 * passed in as a flag here because if the corresponding mtx_init() was 891 * called with MTX_QUIET set, then it will already be set in the mutex's 892 * flags. 893 */ 894 void 895 mtx_destroy(struct mtx *m) 896 { 897 898 if (!mtx_owned(m)) 899 MPASS(mtx_unowned(m)); 900 else { 901 MPASS((m->mtx_lock & (MTX_RECURSED|MTX_CONTESTED)) == 0); 902 903 /* Perform the non-mtx related part of mtx_unlock_spin(). */ 904 if (LOCK_CLASS(&m->mtx_object) == &lock_class_mtx_spin) 905 spinlock_exit(); 906 else 907 curthread->td_locks--; 908 909 /* Tell witness this isn't locked to make it happy. */ 910 WITNESS_UNLOCK(&m->mtx_object, LOP_EXCLUSIVE, __FILE__, 911 __LINE__); 912 } 913 914 m->mtx_lock = MTX_DESTROYED; 915 lock_destroy(&m->mtx_object); 916 } 917 918 /* 919 * Intialize the mutex code and system mutexes. This is called from the MD 920 * startup code prior to mi_startup(). The per-CPU data space needs to be 921 * setup before this is called. 922 */ 923 void 924 mutex_init(void) 925 { 926 927 /* Setup turnstiles so that sleep mutexes work. */ 928 init_turnstiles(); 929 930 /* 931 * Initialize mutexes. 932 */ 933 mtx_init(&Giant, "Giant", NULL, MTX_DEF | MTX_RECURSE); 934 mtx_init(&sched_lock, "sched lock", NULL, MTX_SPIN | MTX_RECURSE); 935 mtx_init(&proc0.p_mtx, "process lock", NULL, MTX_DEF | MTX_DUPOK); 936 mtx_init(&devmtx, "cdev", NULL, MTX_DEF); 937 mtx_lock(&Giant); 938 } 939 940 #ifdef DDB 941 void 942 db_show_mtx(struct lock_object *lock) 943 { 944 struct thread *td; 945 struct mtx *m; 946 947 m = (struct mtx *)lock; 948 949 db_printf(" flags: {"); 950 if (LOCK_CLASS(lock) == &lock_class_mtx_spin) 951 db_printf("SPIN"); 952 else 953 db_printf("DEF"); 954 if (m->mtx_object.lo_flags & LO_RECURSABLE) 955 db_printf(", RECURSE"); 956 if (m->mtx_object.lo_flags & LO_DUPOK) 957 db_printf(", DUPOK"); 958 db_printf("}\n"); 959 db_printf(" state: {"); 960 if (mtx_unowned(m)) 961 db_printf("UNOWNED"); 962 else { 963 db_printf("OWNED"); 964 if (m->mtx_lock & MTX_CONTESTED) 965 db_printf(", CONTESTED"); 966 if (m->mtx_lock & MTX_RECURSED) 967 db_printf(", RECURSED"); 968 } 969 db_printf("}\n"); 970 if (!mtx_unowned(m)) { 971 td = mtx_owner(m); 972 db_printf(" owner: %p (tid %d, pid %d, \"%s\")\n", td, 973 td->td_tid, td->td_proc->p_pid, td->td_proc->p_comm); 974 if (mtx_recursed(m)) 975 db_printf(" recursed: %d\n", m->mtx_recurse); 976 } 977 } 978 #endif
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